The present invention relates to an image reader, for example, for obtaining an image data corresponding to image information of the object as well as an image forming apparatus capable of forming the image corresponding to image information read by the image reader.
An image reader includes a transparent glass plate for holding the subject (original holding section), lighting lamp for illuminating the subject set to the original holding section (lighting unit), CCD sensor for receiving and photoelectrically converting the reflected light from the subject illuminated by the lighting unit (photoelectric converting element), optical set disposed between the original holding section and the photoelectric converting element (mirror and image forming lens), etc.
In this kind of image reader (image reading section), a few mirrors contained in the lighting unit and the optical set are installed along the shorter side of the original table, and are moved in the direction of other orthogonal one side (of the original table) at a predetermined speed. With this configuration, the image of the subject is taken out as a contrast of the light with respect to the elongated illuminated range in the first direction (shorter side of the original table) defined by the illuminating light from the lighting lamp and is guided to the light receiving surface of the CCD sensor. In addition, by allowing the lighting lamp to be moved in the second (other side) direction where the two lights from the first and the second (other one side) directions cross at right angles, the image of the overall region of the subject to be read is taken out as a contrast of light and is guided to the light receiving surface of the CCD sensor.
In the image reader (image reading section) described above, the resolution of the image (optical image) formed on the light receiving surface (photosensitive surface of the photosensitive material) of the CCD sensor is optimized by adjusting the distance between the front-side main plane of the image forming lens and the surface with which original is brought in contact of the two surfaces of the glass plates of the original holding section, distance between the rear-side main plane of the image-forming lens and the light receiving surface of the CCD (photosensitive surface of the photosensitive drum), and the position for a plurality of subjects to be adjusted represented by the gradient of mirrors of the optical set or the fixed position of the CCD sensor, and the like.
The image information photoelectrically converted by the CCD sensor is used for modulating the intensity of laser beam outputted from the laser exposure device of the exposure system in forming the latent image onto the photosensitive material, for example, in the digital copying machine, and the like.
By the way, in an analog copying machine in which a return mirror is arranged in place of the CCD sensor to guide the reflected light from the subject directly to the photosensitive material as it is, the image reading section having the original holding section, lighting unit, and optical set has the similar configuration.
Now, in order to read the image information of the original in full colors, today, a color image reader using a color CCD sensor has been put into practical use.
However, when the three-line CCD sensor is used for the color CCD sensor, the image information of the original projected on the three line sensors of R (red), G (green), and B (blue) by the reducing lens is irradiated on one line sensor located on an optical axis of the reducing lens and two line sensors located at a predetermined distance with respect to the optical axis of the reducing lens in the plane that intersects the optical axis of the reducing lens at right angles.
Consequently, photoelectrically converting the image of the original projected to the three-line CCD sensor provides sizes (widths) varied in accordance with each color component by the lateral chromatic aberration of the reducing lens. As a result, in the image signal outputted, color deviation must be included. The magnitude of color deviation associated with lateral chromatic aberration is able to be alleviated by optimally designing the reducing lens, but because of the limit of lens performance and cost increase, color deviation is unable to be completely removed. In addition, because the resolution of the image forming apparatus has been improved, color deviation of the image becomes conspicuous even if slight lateral chromatic aberration remains.
In Jpn. Pat. Appln. KOKAI Publication No. 10-42157, there are disclosed an image processing method and its apparatus for correcting color deviation resulting from vibration of structural elements of the image reader.
The image processing method disclosed in the above-mentioned patent publication relates to a method for reading an image of xe2x80x9cMansenxe2x80x9d original (black-and-white pair-line chart in which black fine lines of a predetermined width extending in the sub-scanning direction are drawn at predetermined intervals on white paper), finding the color deviation amount from the intersecting point of xe2x80x9cMansenxe2x80x9d data read with the predetermined threshold value, interpolating them and preparing the color deviation amount table that corresponds to each pixel position, correlating the color deviation amount table with the image data of pixels in the vicinity of the noted pixel, and thereby correcting color deviation of the noted pixel (position of the noted pixel on the color deviation amount table).
However, the image processing method disclosed in the above-mentioned patent publication has a problem of greatly varying the calculation results when the output data of two pixels in front and behind are affected by noise because the positional deviation amount is found from the two pixels before and behind the predetermined threshold value when the positional deviation amount is calculated from the xe2x80x9cMansenxe2x80x9d data. Further, the above-mentioned method is unable to find the position deviation amount of all the pixels in one process because it is the upper limit to obtain the frequency xc2xd the pixel cycle when the xe2x80x9cMansenxe2x80x9d chart is used for calculating the position deviation amount with the Shannon""s sampling theorem taken into account, and the method must interpolate the intermediate data by the use of the data obtained. In addition, because the method needs memory for storing the color deviation amount corresponding to each pixel position, it also has a problem in that it needs a memory for storing the color deviation amount for a total of 3 lines in which the two remaining colors are added to one reference color.
Accordingly, it is an object of the present invention to provide a color image reader for generating image signals utilized for a color image forming apparatus that can suppress generation of image color deviation which depends on the distance between the 3-line CCD sensor and the optical axis of the reducing lens.
The present invention provides a color image reader comprising:
a reading object holder, having plate shape and which can transmit light, for holding the subject to be read;
a lighting device for illuminating the subject to be read on the reading object holder;
a reducing lens for providing convergence to the image light from the reading object;
a 3-line CCD sensor for receiving the image light with convergence given by the reducing lens and outputting three electrical signals corresponding to the image light; and
a lateral chromatic aberration correction circuit for designating one output signal of the three output signals outputted from the 3-line CCD sensor to the reference, comparing the two remaining output signals with the output signal used for the reference, and providing a predetermined correction to the two remaining output signals.
The present invention provides an image reading method having:
a reading object holder, having plate shape and rectangular form with four sides, for holding a reading object;
a lighting device for illuminating the reading object on the reading object holder;
a reducing lens for providing convergence to the image light from the reading object;
a 3-line CCD sensor containing three line sensors and receiving the image light in the form of band extending in the first direction from the reading object with convergence given by the reducing lens for each color component, and outputting electrical signals corresponding to the respective lights; and
a lateral chromatic aberration correction circuit for designating one output signal of the three output signals outputted from the 3-line CCD sensor to the reference, comparing the two remaining output signals with the output signal used for the reference, and providing a predetermined correction to the two remaining output signals, and
comprising the steps of:
reading the test chart images;
determining output signals from individual line sensors corresponding to the test chart images; and
comparing the two remaining output signals with the output signal used for the reference, and providing a predetermined correction to the two remaining output signals with one of the three output signals outputted from the individual line sensors of the 3-line CCD sensor used as a reference.
Furthermore, the present invention provides a color image forming apparatus comprising:
a color image reader including;
a reading object holder, having plate shape and can transmit light, for holding the reading object;
a lighting device for illuminating the reading object on the reading object holder;
a reducing lens for giving convergence to the image light from the reading object;
a 3-line CCD sensor for receiving the image light with convergence given by the reducing lens and outputting three electrical signals corresponding to the image light; and
a lateral chromatic aberration correction circuit for designating one output signal of the three output signals outputted from the 3-line CCD sensor to the reference, comparing the two remaining output signals with the output signal used for the reference, and providing a predetermined correction to the two remaining output signals;
an exposure device for irradiating the exposed light with the light intensity varied in correspondence with the output image signal generated by the color image reader to a predetermined position;
the first and the second image forming apparatus in which each of the image forming apparatuses comprises a photosensitive material which is a light receptor, a developing apparatus for selectively supplying the visualized material to the photosensitive material, a transcription apparatus for transcribing the visualized material from the photosensitive material to the transferred material, wherein individual image forming apparatus which supply the visualized material by the developing apparatus to the latent image formed on the photosensitive material by the exposed light irradiated from the exposure apparatus to visualize the image and form the visualized image are disposed in a predetermined arrangement, and form a plurality of toner images for each color component in correspondence with the output image signals for each color component supplied from the color image reader in conformity to time series;
a transferred material conveying mechanism located at a predetermined position with respect to each of the transcription apparatus of the first and the second image forming apparatus and conveying the visualized image formed by the first and the second image forming apparatus transcribably onto the transferred material while the transferred material fed from the storage section is being conveyed; and
a fixing apparatus including a heating mechanism and pressurizing mechanism, for fixing the visualized image transferred on the transferred material to the transferred material being conveyed by the transferred material conveying mechanism.